Irrigation

In many parts of New Zealand, reliable irrigation will be essential to maximising future agriculture and horticulture production. Many rivers and streams are already under pressure, so at Trustpower we recognise that a key part of the solution is to integrate water use for both generation and irrigation, without impacting on generation capability and environmental commitments.

Utilising Lake Coleridge for irrigation

Lake Coleridge is a natural lake, west of Christchurch, managed by Trustpower and feeding Coleridge Power Station. It is near to and capable of supplying some of mid-Canterbury’s largest developing and established irrigation schemes.

In 2012, Trustpower secured a variation to the existing Water Conservation Order on the Rakaia River. With the change, water can be stored in Lake Coleridge for irrigation supply as well as for generation (there was no change to water allocation criteria protecting environmental aspects of the river system). Lake Coleridge storage, together with river take, can potentially provide high levels of reliability for up to 100,000 hectares (ha) of irrigation.

CPW intends to develop a new irrigation scheme on the north bank of the Rakaia River, with a potential 60,000ha supply area. This scheme accesses river flow with low reliability, so storage from Lake Coleridge will be key.

Highbank Pumping

Highbank Pumping Station stands alongside our existing Highbank Power Station and supplies irrigation water to BCI via the Rangitata Diversion Race. The pumping station was especially built to supply BCI with irrigation water.

Water is extracted from the Rakaia River, into a short canal alongside the existing Highbank Power Station tailrace and into the new pumping station. It’s then piped up the existing penstock and into the Rangitata Diversion Race for delivery to farmers. We envisage the pumping station will eventually be capable of supplying the Rangitata Diversion Race with 8 cubic metres per second of irrigation water.

Towards integrated irrigation in Canterbury

There is potential for Lake Coleridge to be integrated into the wider Canterbury irrigation water infrastructure. This could encompass both existing and future infrastructure, such as additional storage facilities and supply systems.

Trustpower is working with Environment Canterbury and irrigation users to develop infrastructure plans that would allow water to be conveyed and supplied over a much greater area of Mid and South Canterbury. A key focus is progressive sustainable development, over a number of years.

Once coupled with integrated infrastructure, Lake Coleridge would be fundamental to opening new irrigation areas, allowing water to be assigned to new users without negative impact on existing users. Integration means water could be traded amongst users, ensuring the highest value use.